This invention relates to forming holes with a laser beam and, in particular, to drilling circular holes with noncircular or irregular laser beams.
Lasers may be used to drill holes in or otherwise machine a work piece. For example, a laser may be used to machine metal foils to produce print heads for inkjet printers. Lasers may also be used to machine dielectric materials to form wave guides or microoptical structures in the materials.
For some laser drilling applications, such as laser drilling of inkjet nozzles, it is preferable for the drilled holes to be circular. The shape of a hole formed by a focused laser may depend on the shape of the laser beam. Irregularities in the shape of the laser beam and its intensity distribution may result in a non-circular hole being drilled.
Existing methods for drilling roughly circular holes using laser beams may employ a technique known as trepan drilling. In trepan drilling a laser beam is translated in a circular pattern on the work piece. While trepan drilling reduces the effects of localized irregularities in the intensity distribution of the drilling laser, it can not correct for all beam irregularities, especially for irregularities occurring near the edge of the beam cross-section. If, for example, the beam cross-section is elliptical then any hole drilled by trepan drilling, in which the beam is translated in a circular pattern, will also be elliptical. This is especially true for very small holes. Indeed, because trepan drilling moves the beam along a circular course to drill the circular hole, it is difficult to make a small hole. It would be impossible, for example, to make a hole by trepan drilling that has the same size as the active area of the laser beam cross-section.
Another technique that is used for drilling circular holes is to use the laser to project an image of a circular aperture on to the work piece. This method may, for example, use a circular mask to block portions of the beam which are outside of the mask. This technique is undesirable, however, as the energy in the masked area is not applied to the work piece.
The present invention is embodied in a method and apparatus for machining a work piece with a laser beam to form a circular hole in the work piece.
According to an aspect of the present invention, a laser generates a laser beam having a beam area and a beam axis within the beam area. A beam rotator rotates the laser beam about the beam axis and directs the rotating laser beam toward the work piece.
According to another aspect of the present invention, the beam rotator rotates at an angular velocity and causes the laser beam to rotate at twice that angular velocity.
According to another aspect of the present invention, the laser beam is a pulsed laser beam and multiple pulses are applied to the work piece to drill a single hole.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention.